I would first fix the power amp problems before working on the FX and the preamps. Almost all of the Kustom power amps use the same basic architecture, and are really basic. All the major manufacturers have used the same basic design for the past 40-50 years. You should not have any problem getting it figured out.
If the power amp is overheating, then there probably is a balance problem between the two halves of the output section. This can also be the source of the hum and of the voltage on the output. I don't know if you have a light bulb limiter available, but if you do, use it until you get the power amp working. Check all of the transistors in the power amp and take voltage readings to see if they come close to the listed schematic values.
The 1N3754 diode that clips to the heat sink is fragile, so be careful while you are working on the amp.